/* ============================================
   LAYOUT - Abstraction Cheatsheet
   Navigation, grid system, responsive design
   ============================================ */

/* ============================================
   APP LAYOUT
   ============================================ */
.app {
    display: flex;
    min-height: 100vh;
}

/* ============================================
   HEADER
   ============================================ */
.header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--header-height);
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-default);
    z-index: var(--z-fixed);
    display: flex;
    align-items: center;
    padding: 0 var(--space-lg);
    backdrop-filter: blur(12px);
    background: rgba(22, 27, 34, 0.85);
}

[data-theme="light"] .header {
    background: rgba(255, 255, 255, 0.85);
}

.header__logo {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-weight: 700;
    font-size: var(--text-lg);
    color: var(--text-primary);
}

.header__logo-icon {
    width: 32px;
    height: 32px;
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-weight: 700;
    font-size: var(--text-lg);
}

.header__actions {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    margin-left: auto;
}

.header__menu-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--text-primary);
    cursor: pointer;
    padding: var(--space-sm);
    border-radius: var(--radius-md);
    transition: background var(--transition-fast);
}

.header__menu-toggle:hover {
    background: var(--bg-tertiary);
}

/* ============================================
   SIDEBAR NAVIGATION
   ============================================ */
.sidebar {
    position: fixed;
    top: var(--header-height);
    left: 0;
    bottom: 0;
    width: var(--sidebar-width);
    background: var(--bg-secondary);
    border-right: 1px solid var(--border-default);
    overflow-y: auto;
    z-index: var(--z-sticky);
    padding: var(--space-lg);
    display: flex;
    flex-direction: column;
}

.sidebar__search {
    position: relative;
    margin-bottom: var(--space-lg);
}

.sidebar__search-input {
    width: 100%;
    padding: var(--space-sm) var(--space-md);
    padding-left: 2.5rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-default);
    border-radius: var(--radius-md);
    color: var(--text-primary);
    font-size: var(--text-sm);
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.sidebar__search-input::placeholder {
    color: var(--text-muted);
}

.sidebar__search-input:focus {
    border-color: var(--accent-blue);
    box-shadow: 0 0 0 3px var(--glow-blue);
    outline: none;
}

.sidebar__search-icon {
    position: absolute;
    left: var(--space-sm);
    top: 50%;
    transform: translateY(-50%);
    color: var(--text-muted);
    pointer-events: none;
}

.sidebar__search-shortcut {
    position: absolute;
    right: var(--space-sm);
    top: 50%;
    transform: translateY(-50%);
    font-size: var(--text-xs);
    color: var(--text-muted);
    background: var(--bg-elevated);
    padding: 2px 6px;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-default);
}

/* Navigation Tree */
.nav-tree {
    list-style: none;
    padding: 0;
    margin: 0;
    flex: 1;
    overflow-y: auto;
}

.nav-part {
    margin-bottom: var(--space-lg);
}

.nav-part__header {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: var(--space-sm) 0;
    font-size: var(--text-sm);
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    cursor: pointer;
    user-select: none;
    transition: color var(--transition-fast);
}

.nav-part__header:hover {
    color: var(--text-primary);
}

.nav-part__icon {
    width: 16px;
    height: 16px;
    transition: transform var(--transition-fast);
}

.nav-part.collapsed .nav-part__icon {
    transform: rotate(-90deg);
}

.nav-part.collapsed .nav-part__items {
    display: none;
}

.nav-part__items {
    list-style: none;
    padding: 0;
    margin: 0;
}

.nav-item {
    position: relative;
}

.nav-item__link {
    display: block;
    padding: var(--space-sm) var(--space-md);
    padding-left: var(--space-lg);
    font-size: var(--text-sm);
    color: var(--text-secondary);
    text-decoration: none;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
    border-left: 2px solid transparent;
}

.nav-item__link:hover {
    color: var(--text-primary);
    background: var(--bg-tertiary);
    text-decoration: none;
}

.nav-item__link.active {
    color: var(--accent-blue);
    background: var(--glow-blue);
    border-left-color: var(--accent-blue);
}

/* Subsections */
.nav-item__subsections {
    list-style: none;
    padding: 0;
    margin: 0;
    padding-left: var(--space-md);
}

.nav-item__subsection {
    padding: var(--space-xs) var(--space-md);
    padding-left: var(--space-lg);
    font-size: var(--text-xs);
    color: var(--text-muted);
    text-decoration: none;
    display: block;
    transition: color var(--transition-fast);
}

.nav-item__subsection:hover {
    color: var(--text-secondary);
    text-decoration: none;
}

/* ============================================
   MAIN CONTENT AREA
   ============================================ */
.main {
    flex: 1;
    margin-left: var(--sidebar-width);
    margin-top: var(--header-height);
    padding: var(--space-2xl) var(--space-3xl);
    max-width: calc(var(--content-max-width) + var(--sidebar-width) + var(--space-3xl) * 2);
}

.main__content {
    max-width: var(--content-max-width);
}

/* ============================================
   SECTION LAYOUT
   ============================================ */
.section {
    margin-bottom: var(--space-3xl);
    scroll-margin-top: calc(var(--header-height) + var(--space-lg));
}

.section__header {
    margin-bottom: var(--space-xl);
}

.section__title {
    display: flex;
    align-items: center;
    gap: var(--space-md);
}

.section__number {
    font-size: var(--text-sm);
    font-weight: 600;
    color: var(--accent-blue);
    background: var(--glow-blue);
    padding: var(--space-xs) var(--space-sm);
    border-radius: var(--radius-md);
    min-width: 2rem;
    text-align: center;
}

.section__description {
    font-size: var(--text-lg);
    color: var(--text-secondary);
    margin-top: var(--space-sm);
}

/* Part Headers (major sections) */
.part-header {
    text-align: center;
    padding: var(--space-3xl) 0;
    margin-bottom: var(--space-2xl);
    border-bottom: 1px solid var(--border-default);
}

.part-header__number {
    font-size: var(--text-sm);
    font-weight: 600;
    color: var(--accent-purple);
    text-transform: uppercase;
    letter-spacing: 0.1em;
    margin-bottom: var(--space-sm);
}

.part-header__title {
    font-size: var(--text-3xl);
    background: linear-gradient(135deg, var(--text-primary), var(--accent-blue));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* ============================================
   THEME TOGGLE
   ============================================ */
.theme-toggle {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-default);
    border-radius: var(--radius-full);
    padding: var(--space-xs) var(--space-sm);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: var(--space-xs);
    transition: all var(--transition-fast);
}

.theme-toggle:hover {
    border-color: var(--accent-blue);
}

.theme-toggle__icon {
    width: 20px;
    height: 20px;
    color: var(--text-secondary);
}

.theme-toggle__icon--sun {
    display: none;
}

[data-theme="light"] .theme-toggle__icon--sun {
    display: block;
}

[data-theme="light"] .theme-toggle__icon--moon {
    display: none;
}

/* ============================================
   RESPONSIVE DESIGN
   ============================================ */

/* Tablet */
@media (max-width: 1024px) {
    :root {
        --sidebar-width: 240px;
    }

    .main {
        padding: var(--space-xl) var(--space-2xl);
    }
}

/* Mobile */
@media (max-width: 768px) {
    .header__menu-toggle {
        display: flex;
    }

    .sidebar {
        transform: translateX(-100%);
        transition: transform var(--transition-base);
        width: 280px;
        top: 0;
        padding-top: calc(var(--header-height) + var(--space-lg));
    }

    .sidebar.open {
        transform: translateX(0);
    }

    .sidebar-overlay {
        position: fixed;
        inset: 0;
        background: rgba(0, 0, 0, 0.5);
        z-index: calc(var(--z-sticky) - 1);
        opacity: 0;
        pointer-events: none;
        transition: opacity var(--transition-base);
    }

    .sidebar-overlay.visible {
        opacity: 1;
        pointer-events: auto;
    }

    .main {
        margin-left: 0;
        padding: var(--space-lg);
    }

    h1 {
        font-size: var(--text-2xl);
    }

    h2 {
        font-size: var(--text-xl);
    }

    .part-header__title {
        font-size: var(--text-2xl);
    }
}

/* Large Desktop */
@media (min-width: 1400px) {
    .main {
        padding-left: var(--space-3xl);
        padding-right: var(--space-3xl);
    }
}

/* ============================================
   PRINT STYLES
   ============================================ */
@media print {

    .header,
    .sidebar,
    .theme-toggle {
        display: none !important;
    }

    .main {
        margin: 0;
        padding: 1rem;
        max-width: 100%;
    }

    .section {
        page-break-inside: avoid;
    }
}